Abstract CT158: A dose escalation and cohort expansion study of the CDK9 inhibitor KB-0742 in relapsed, refractory and transcriptionally addicted solid tumors

Abstract Background MYC transcriptional deregulation is a hallmark of cancer and is associated with poor clinical outcomes. MYC deregulated solid tumors including non-small cell (NSCLC), small cell lung cancer (SCLC), triple negative breast cancer (TNBC), and ovarian cancer are known for their aggressiveness and frequent relapse. Analysis of a real-world solid tumor cohort including NSCLC (n= 20, 470), SCLC (n=1, 517), TNBC (n=2, 576) and ovarian cancer (n=1, 667) demonstrated MYC family overexpression and/or genomic amplification in 47% to 87% of patients. Although MYC remains difficult to drug, targeting of its cofactors has emerged as an attractive strategy to inhibit MYC oncogenic activity. Cyclin-dependent kinase 9 (CDK9), a MYC cofactor, is a critical regulator of oncogenic MYC expression and activity. KB-0742 is a potent, selective, and orally bioavailable inhibitor of CDK9 with a long plasma half-life. KB-0742 is being evaluated in an ongoing Phase 1/2 study in advanced solid tumors (NCT04718675). Methods The Phase 1/2 study is being conducted in two parts: dose escalation and dose expansion. Part 1 dose escalation comprises patients with relapsed or refractory solid tumors. Part 2 dose expansion comprises patients with solid tumors that have a high prevalence of MYC overexpression including ovarian cancer, NSCLC, TNBC and SCLC. KB-0742 is dosed orally once daily for 3 consecutive days followed by 4 days off on a weekly basis in 28-day cycles until unacceptable toxicity or disease progression. Eligibility criteria include age 18 years acceptable organ function and ECOG PS 2. Up to 170 patients are planned to be enrolled in the study. Primary objectives include evaluation of pharmacokinetics (PK), pharmacodynamics (PD), safety, tolerability, and preliminary anti-tumor activity with the goal of identifying a maximum tolerated dose (MTD). Plasma PK measurements include Cmax, tmax, AUC0-last, accumulation ratio (Racc) and t1/2. Safety data will be evaluated per the National Cancer Institute Common Terminology Criteria for Adverse Events (NCI-CTCAE) v5. 0. RP2D is informed by PD in peripheral blood mononuclear cells using assays to evaluate phosphorylation of the CDK9 substrate serine 2 on the RNA Polymerase II C-terminal domain (pSER2) and CDK9-responsive gene expression. Radiographic tumor response is assessed using RECIST 1. 1 criteria. Exploratory objectives include assessment of KB-0742 PD in tumor tissue and profiling of treatment-related genomic, transcriptomic, and proteomic changes. The study is continuing as planned; the next data analysis will occur in 2024. Citation Format: Miguel Villalona Calero, Mark Agulnik, Monica Mita, Alain Mita, Noah Federman, Drew Rasco, David Spigel, Jia Luo, Glenn Hanna, Gregory Cote, Mohamad A. Salkeni, Rashmi Chugh, Natraj R. Ammakkanavar, Satish A. Shah, Amol Rao, Kamalesh Kumar Sankhala, Richard E. Cutler, Tressa Hood, Luis Carvajal, Crystal MacKenzie, Charles Lin, Jorge DiMartino, Elizabeth A. Olek, Brian Van Tine. A dose escalation and cohort expansion study of the CDK9 inhibitor KB-0742 in relapsed, refractory and transcriptionally addicted solid tumors abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (7Suppl): Abstract nr CT158.